In internal combustion engines, a high compression ratio has a positive effect on the efficiency of the internal combustion engine. A compression ratio is generally understood to be the ratio of the entire cylinder volume before compression with respect to the remaining cylinder volume after compression. In internal combustion engines with external ignition, in particular in spark ignition engines which generally have a fixed compression ratio, a value for the compression ratio must be selected which is only so high that in the full load operating mode what is referred to as “knocking” of the internal combustion engine is avoided. However, for the much more frequently occurring partial load range of the internal combustion engine, that is to say when there is a small cylinder charge, higher values can be selected for the compression ratio without “knocking” occurring. The important partial load range of an internal combustion engine can be improved if the compression ratio can be set in a variable fashion.
DE 10 2010 016 037 A1, which is incorporated by reference herein, discloses an internal combustion engine with an adjustable compression ratio. A connecting rod which has a pin bearing eye and a big end bearing eye can be connected to a crankshaft via the pin bearing eye, and to a cylinder piston of the internal combustion engine via the big end bearing eye. The connecting rod is assigned an eccentric adjustment device which has an eccentric body and eccentric rods.
The eccentric body which is known from DE 10 2010 016 037 A1, which is incorporated by reference herein, has a piston bolt bore which is arranged eccentrically with respect to a center point of the big end bearing eye and has a center point, wherein the piston bolt bore accommodates a piston bolt. The eccentric adjustment device serves to adjust an effective connecting rod length leff, wherein the distance between the center point of the piston rod bore and a center point of the pin bearing eye is to be understood as the connecting rod length. The eccentric rods of the eccentric adjustment device can be moved in order to rotate the eccentric body and therefore to change the effective connecting rod length leff. Every connecting rod is assigned a piston which is displaceably mounted or guided in a hydraulic chamber. In the hydraulic chambers there is a hydraulic pressure which acts on the pistons which are assigned to the eccentric rods, wherein the movement of the eccentric rods is possible or is not possible depending on the quantity of oil in the hydraulic chambers.
The adjustment of the eccentric adjustment device is initiated by the action of mass forces and load forces of the internal combustion engine which act on the eccentric adjustment device when there is a working stroke of the internal combustion engine. During a working stroke, the directions of action of the forces acting on the eccentric adjustment device change constantly. The adjustment movement is assisted by the pistons which are supplied with hydraulic oil and which act on the eccentric rods, whereby the pistons prevent the eccentric adjustment device from being reset by virtue of varying directions of force of the forces acting on the eccentric adjustment device. The eccentric rods which interact with the pistons are connected to the eccentric body on both sides.
The hydraulic chambers in which the pistons are guided can be supplied or filled with hydraulic oil from the pin bearing eye via hydraulic oil feedlines. Non-return valves prevent the hydraulic oil from flowing back out of the hydraulic chambers into the hydraulic oil feedlines. A switching valve is accommodated in a bore of the connecting rod. The hydraulic chambers are connected via hydraulic oil discharge lines to the bore which accommodates the switching valve. The switched position of the switching valve determines which of the hydraulic chambers is filled with hydraulic oil and which of the hydraulic chambers is emptied, wherein the adjustment direction or rotational direction of the eccentric adjustment device depends on this.
As stated, the hydraulic oil which acts on the pistons, guided in the hydraulic chambers, of the eccentric rods, is fed to the hydraulic chambers from the pin bearing eye via the hydraulic oil feedlines, whereby the connecting rod acts on the crankshaft with the pin bearing eye in such a way that a big end bearing shell is arranged between the crankshaft, specifically a crankshaft bearing pin thereof, and the pin bearing eye.
The hydraulic chambers can be vented via the hydraulic oil discharge lines as a function of the switched position of the switching valve. The adjustment direction or rotational direction of the eccentric adjustment device depends on this.
The switching valve which is known from DE 10 2010 016 037 A1, which is incorporated by reference herein, comprises an activation element, a restoring spring and a control piston.
DE 10 2012 112 461 A1, which is incorporated by reference herein, discloses a switching valve for an internal combustion engine with an adjustable compression ratio according to the preamble of patent claim 1. The switching valve which is disclosed in said document has a switching element and a connecting section, wherein the switching element is guided in the connecting section so as to be moveable between the two switched position by forming a gap between a surface of the switching element and a corresponding guide face of the connecting section. The effectiveness of the switching valve is dependent on the tightness thereof.
Although the adjustment direction or rotational direction of the eccentric adjustment device can already be effectively influenced with the switching valves which are known from the prior art, there is a need for an improved, more effective switching valve.